Circuit breaker with external heater

ABSTRACT

The invention is embodied in an overload circuit breaker or protective switch of the type in which a member responsive to an electrical overload opens the circuit through the switch by latching open the switch contacts. A resetting member, when actuated, serves to reclose the switch contacts. The circuit breaker, however, is characterized by a set of auxiliary or secondary switch contacts connected electrically in series with the primary circuit breaker contacts. The movable contact arm or blade carrying the movable auxiliary contact is segmented so that the contact it carries can be electrically connected to an electric heater wrapped about the thermally responsive operator for the main switch contacts and the arm can, nevertheless, be supported by the electrically conductive housing or chassis, as can the operator for the main switch, without adversely affecting the trip-free reset operation of the breaker.

United States Patent inventors Cleon F. Frey Sebastian, Fla.; Myron I".Melvin, Indianapolis, Ind. Appl. No. 65,100 Filed Aug. 19, 1970 PatentedDec. 21, 1971 Assignee Cornel International Corporation Bayamon, P.R.

CIRCUIT BREAKER WITH EXTERNAL HEATER l Claiin, 3 Drawing Figs.

3,358,099 12/1967 Bellomayre 2,191,588 2/1940 Sattler ABSTRACT: Theinvention is embodied in an overload circuit breaker or protectiveswitch of the type in which a member responsive to an electricaloverload opens the circuit through the switch by latching open theswitch contacts. A resetting member, when actuated, serves to reclosethe switch contacts. The circuit breaker, however, is characterized by aset of auxiliary or secondary switch contacts connected electrically inseries with the primary circuit breaker contacts. The movable contactarm or blade carrying the movable auxiliary contact is segmented so thatthe contact it carries can be electrically connected to an electricheater wrapped about the thermally responsive operator for themainswitch contacts and the arm can, nevertheless, be supported by theelectrically conductive housing or chassis, as can the operator for themain switch, without adversely affecting the trip-free reset operationof the breaker.

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i I E 4: 3 \Y.\ S\ \\i 20 25 204/ ls INVENTORS 5 [Zea/v F [25v a BY MmouF MEL WA] -3- MmMLUMMf/W ATTORNEYS 1 CIRCUIT BREAKER WITH EXTERNALHEATER BACKGROUND OF THE INVENTION Circuit breakers, adapted to open thecircuit through electrical appliances or television receivers or thelike upon an electrical overload are well known in the prior art. Suchoverload protective switches are customarily provided with the trip-freefeature. This trip-free quality prevents the user of the appliance frommanually retaining the circuit breaker contacts closed under overloadconditions by holding or jamming the reset button in actuated position.Customarily, this reset feature is provided by arranging the resetmechanism so that the circuit breaker contacts are blocked open untilthe reset button is released. An example of this type of structure isdis closed in Frey U.S. Pat. No. 2,948,787.

Since rapidity of response is a primary consideration in overloadprotective devices of this type, of necessity the thermally responsivecomponent, usually a bimetal blade which responds to the heat generatedby an electrical current overload, must have minimum thermal inertia,that is, in the case of a bimetal blade, relatively low mass. Asensitive, rapidly responsive bimetal member of low mass, however, has arelatively low force-deflection ratio, or work output per unittemperature variation. This low work output characteristic opposes theproviding of the switch structure with heavy duty contacts to permit itto carry heavy overload currents without arcing and welding of thecontacts together. A portion of the danger of arcing and welding of thecontact structure can be eliminated if the reclosing of the contacts,after release of the reset button, is completed while no electricalpotential exists across the contacts. In conventional trip-free resetcircuit overloadswitches, although the contacts are held open while thereset member is depressed, when it is released, assuming the overloadhas not been removed, the contacts are reclosed on the full overloadcurrent. The relatively massive, heavyduty contacts required for thistype of operation require heavier bimetal thermally responsive membersand rapidity of response is thus sacrificed. It is, therefore, desirableto provide an overload circuit breaker in which an auxiliary pair ofcontacts are in series with the primary breaker contacts. Theseauxiliary contacts are held open mechanically as long as the resetbutton is depressed to provide the breaker with the tripfree feature,the primary contacts being reclosed, with no potential across them, upondepressing of the reset button. Upon release of the reset button, theauxiliary contacts are reclosed with potential across them, however,since these auxiliary contacts, as distinguished from the primarybreaker contacts, are not operated by a relatively light bimetal member,they may be of a heavy-duty, massive type without sacrificing responsetime of the breaker.

This structural form has the advantages referred to above, however,where an external electrical heater is used to wrap the bimetal blade,rather than the internally generated heat when current passes throughthe bimetal blade, circuit connection difficulties occur. The use of theexternal bimetal heater type of construction is desireable in someEuropean countries, for example, where a 220 volt circuit is utilized,less current being available for heat generation in the bimetal for agiven power input. The circuit difficulties referred to come aboutbecause of the necessity to have the circuit through the heaterelectrically isolated from the switch chassis or housing. if it is notso isolated, then the chassis, usually formed of electrically conductivemetal, must include elaborate, electrically insulated pivotal mountingsfor both the bimetal blade and the blade operating the auxiliarycontacts, otherwise the chassis would short the auxiliary contactsduring resetting of the main contacts and the necessary trip-free resetwould be eliminated.

SUMMARY OF THE INVENTION the present invention concept utilizes asegmented arm or blade whose auxiliary-contact carrying tip iselectrically isolated from the remainder of the blade which engages, forpivotal, knife-edge support, the metal chassis or housing of the switch.The chassis does not form a portion of the circuit through the heaterand the auxiliary and main set of contacts, so that the pivotallysupported arms or blades for these contacts can directly engage thechassis without electrical insulating supports for the blades beingrequired. Further, the chassis or housing, since it is not in thecircuit through the assembly, does not short out the auxiliary contactsduring the reset operation and the necessary trip-free reset feature isretained.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENT Referring to the drawings, reference numeral 10 indicates abase plate, formed of electrical insulating material, the base platehaving mounted thereon a metal chassis or housing which includes a topplate 11, end plates 12 and 13 and a side plate 14, the side platehaving portions cut away as indicated. An enclosing casing, indicated inbroken lines and identified generally at 15, encloses the chassis.Extending through the base 10 and mounted thereon is a conductive memberhaving one end 16 formedto provide the stationary contact of the primarycircuit breaker switch structure, the other end 17 of the conductivemember extending exteriorly of the housing to provide a terminal lug.

The housing top plate is provided with an aperture 18, one margin ofwhich receives a clip 19 formed of bimetal and arranged to deflect, uponan increase in temperature, in the direction indicated by the arrowin;FlG. 1. Supported between the lower end of the clip 19 and anappropriately notched and slotted portion of the housing end wall 12 isa tripping element 21 all or a portion of which is formed of bimetalarranged to deflect upwardly, as indicated by the arrow in FIG. 1, uponan increase in its temperature. An electric heater 20 is wrapped aroundthe bimetal tripping element and wires 20a and 20b connect opposite endsof the heater to the member 23 and the free end 32 of the member 31,bdth subsequently described. As will be evident from FIG. 1, thetripping element 21 is supported under elastically deforming compressivestress and when the temperature of the thermally responsive bimetalreaches a predetermined point, the tripping element will snap from itsstable position shown in solid lines in FIG. 1 to its stable positionshown in broken lines in FIG. 1, while'the overload current traversingthe heater 20 provides the temperature a blade 23, formed at its freeend to provide a movable contact 24 which cooperates with the stationarycontact 16, the contacts 24 and 16 forming the primary contacts of thecircuit breaker assembly. As previously mentioned, the sidewall 14 hasan extensive cut away portion, indicated at 14a in FIG. 1, and extendinginto this cut away portion, generally in the plane of the sidewall 14 isa member 25. The electrically conductive member 25 has a lower portion25a which extends through the base 10 and forms a terminal lug shapedidentically to the lug 17. The upper end of the member 25 is bent at aright angle to the body of the member and this flanged portion extendsinto the housing to form the electrical contact portion 25b.

The resetting means for returning the tripping element from its brokenline position to its solid line position of FIG. 1 (such resettingoperation being shown in FIG. 2) includes a reset pin 26 which is freelyreceived within an aperture in the upper plate 11 of the housing 15 anda shoulder 26a on the pin prevents its complete withdrawal from thehousing. A reduced tip portion 27 of the pin extends freely through anaperture in the top plate 11, with the shoulder 29 limiting the depth ofinsertion of the pin into the housing. A segmented, resilient blade 31extends beneath the undersurface of the top plate 1 1 and extendsthrough the aperture 18 to the exterior of the housing. The exteriorlyextending portion 31a of the blade is formed in upwardly offsetconfiguration and the tip of the blade, indicated at 31b, is reduced andextends through an accommodating slot in the adjacent portion of the topplate 11. Since the blade is resilient, the offset portion 31a is formedso that the blade is urged against the leftward margin (as viewed inFIG. 1) of the aperture 18 and into engagement with the tip 27 of thereset pin. The free end, indicated at 32 in FIG. 1, is also urged, bythe resiliency of the elongated element, into engagement with the faceof the flange portion 25b of the element 25. Interposed between the freeend 32 and the remainder of blade 31 is a section 320 formed ofelectrical insulating material, this portion 32a of the blade serving telectrically isolate the free eiid 32 from the remainder of the blade31.

The electrical circuit through the circuit breaker is shown in FIG. 3and proceeds from the lug 17, through contacts 16-24, blade 23 andthrough the heater 20. The circuit then proceeds via wire b to the freeend 32 of the blade 31, then through flange b and element 25 to theother terminal 25a. The flange 25b and tip 32 serve as an auxiliary setof contacts in series with primary contacts 24-16.

In operation, upon the occurrence of an overload current through thecontacts 16-25, the heater 20 will cause the tripping element to snapfrom its solid line position of FIG. 1 into its broken line position,opening the contacts. As will be evident from FIG. 2, by depressing thereset pin 26, the engagement of the underface of the element 31 with thetripping element will displace the tripping element and snap it into itsstable position in which the contacts 16-24 are closed. As will beevident from a comparison of FIGS. 1, 2 and 3, when the reset pin isdepressed, the consequent elastic deformation of the element 31separates the contact surface 32 from the contact flange 25b so that, aslong as pin 26 is depressed, auxiliary contacts 25b-32 are open when thetripping element is moved from its stable position indicated at brokenlines in FIG. 2 to its solid line position in which the contacts 16-24are closed. If the reset button is held in depressed position, thecontacts 32 and 25b remain separated and there is no electricalcontinuity between the lugs 25:: and 17. The primary contacts 16 and 24are thus always reclosed under open circuit conditions and the switchingstructure is trip free in that the circuit through the switching deviceis maintained open as long as the reset button is held in actuated ordepressed position. When the reset button is released the restoringforce generated by the elastic deformation of the element 31 moves thereset pin 26 back to its position of FIG. 1 and brings the contactsurface 32 again into engagement with the contact member 25b.

From the foregoing it will be evident that the switching device is tripfree and that, even though an exterior heater (20) is utilized to warptripping element 21 to its actuated position, because the element 31 issegmented, isolating electrically its free end 32 from that portionengaging the chassis, the metallic chassis is not part of the circuit ofthe device, as evident from the FIG. 3, and insulating supports need notbe utilized between the chassis and the element 31 or between thechassis and tripping member 21.

We claim: 1

l. A trip-free overload circuit breaker including a housing and aprimary stationary contact within the housing, a bimetal trippingelement supported by the ;housing movable between two stable positions,and with a primary movable contact cooperating with the primarystationary contact and movable by the tripping element into and out ofengagement with the stationary contact, an electrical heater connectedin series with said primary contacts for moving said tripping element toone of its stable positions from the other upon a current overloadthrough said contacts, a reset pin supported for movement into and outof the housing with the pin being manually movable from a deactuatedposition to an actuated position to displace the tripping element fromsaid one of its stable positions to the other, a unitary means forurging said reset pin from its actuated to its deactuated position andfor removing the electrical potential from across said movable andstationary contacts as said reset pin is moved into its actuatedposition, said means comprising a segmented resilient blade pivotallysupported on the housing, the free end of said blade being electricallyisolated from its supported end, an auxiliary set of contacts, one ofsaid auxiliary contacts being carried on the free end of said segmentedblade, one end of said heater being electrically connected to said freeend of said blade and the opposite end of said heater being electricallyconnected to said primary movable contact.

1. A trip-free overload circuit breaker including a housing and a primary stationary contact within the housing, a bimetal tripping element supported by the housing movable between two stable positions, and with a primary movable contact cooperating with the primary stationary contact and movable by the tripping element into and out of engagement with the stationary contact, an electrical heater connected in series with said primary contacts for moving said tripping element to one of its stable positions from the other upon a current overload through said contacts, a reset pin supported for movement into and out of the housing with the pin being manually movable from a deactuated position to an actuated position to displace the tripping element from said one of its stable positions to the other, a unitary means for urging said reset pin from its actuated to its deactuated position and for removing the electrical potential from across said movable and stationary contacts as said reset pin is moved into its actuated position, said means comprising a segmented resilient blade pivotally supported on the housing, the free end of said blade being electrically isolated from its supported end, an auxiliary set of contacts, one of said auxiliary contacts being carried on the free end of said segmented blade, one end of said heater being electrically connected to said free end of said blade and the opposite end of said heater being electrically connected to said primary movable contact. 